Gas turbines may include a compressor for compressing air, a combustor for producing a hot gas by burning fuel in the presence of the compressed air produced by the compressor, and a turbine for expanding the hot gas to extract shaft power. The combustor may be operated such that a low level of emissions, such as oxides of nitrogen (NOx), are produced by the combustor.
In order to reduce the amount of NOx emissions, a lean-premix fuel may be provided to the combustor. A fuel-lean premix may include fuel premixed with an excess of air (e.g., air in a quantity more than stoichiometrically required for combustion). While the fuel-lean premix may reduce the amount of NOx emissions, high frequency combustion instabilities, commonly referred to as “high frequency dynamics” or “screech oscillations,” may result from burning rate fluctuations inside the combustors when the fuel-lean premix is burned in the combustors. These burning rate fluctuation instabilities may create pressure waves (also referred to as acoustic energy) that may damage the combustor.
One way to reduce these damaging pressure waves is to operate the combustor at maximum power and at standard atmospheric conditions, and design the combustor such that the frequency of pressure waves does not coincide with the natural frequency of oscillation of the sheet metal of the combustor. However, gas turbines may generally operate to provide a wide range of output power under a wide range of operating temperature and pressure, and, as a result, pressure waves having a range of frequencies may be generated in the combustor. It may, therefore, be difficult to design a combustor such that the frequency of pressure waves does not coincide with the natural frequency of oscillation of the sheet metal of the combustor.
What is needed, then, is a combustor of a gas turbine that may produce low level NOx emissions and dampen the generated acoustic energy while operating over a wide range of operating temperatures and pressures.